The present invention relates to an adjusting device for the blast pressure in the cooling nozzles of a glass tempering apparatus, said device comprising at least two blowers, each with its own vane adjuster, blow ducts between the blowers and an air distribution chamber, and a by-pass duct linking said blow ducts.
With this type of prior known adjusting device, the vane adjustment may cover a pressure range that is sufficient for glass thicknesses of 4-12 mm. The attached FIG. 4 illustrates the relationship between glass thickness and required pressure in a semi-logarithmic scale. The high pressure readings required for 4 mm thick glasses are achieved when both blowers are running and the required adjustment is effected by setting the vane angle of vane adjusters. The blast pressure required for glass thicknesses of 5-12 mm is accomplished by keeping one of the blowers stopped with its vane adjuster shut off and by regulating the vane adjuster of a rotating blower. The adjustment ratio of a vane adjuster is in the order of 1:100. Even when shut off, said vane adjuster does not completely close the flow channel (=blower intake port), but said 1/100 of the pressure remains acting on the nozzles. As a result of this and the adjustment ratio of a vane adjuster, this prior known system cannot reach sufficiently low pressures to make it possible to anneal or temper also glasses having a thickness of 15 mm and 19 mm by using the same pressure regulation system. As seen from the curve of FIG. 4, the pressure range required by these glass thicknesses cannot be reached either, even if the vane adjuster of a stopped blower were opened all the way while keeping the vane adjuster of a rotating blower shut off. It is prior known to provide the above type of apparatus with a separate propeller fan whose pressure range is suitable for tempering glass sheets having a thickness of 10-19 mm. This incurs extra equipment costs and operation is more complicated since different cases require the use of different blower systems. Neither is it possible to effect continuous control of blast pressure over the maximum output of a propeller fan. This would be necessary, however, if e.g. a 10 mm glass were to be cooled at a constant cooling rate.
It is also prior known to employ an inverter or direct-current operation for controlling the pressure over an entire desired pressure range but such arrangements are highly expensive and sophisticated and thus also given to malfunctions.
An object of the invention is to further develop this prior know pressure adjusting device so that, by means of a mere vane adjustment, it is possible to cover a pressure range (typically 7000-5 Pa) that is sufficient for tempering glasses having a thickness of 4-19 mm.
This object is achieved by means of an adjusting device of the invention on the basis of the characterizing features set forth in the annexed claims.